<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Channels</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REL="HOME"
TITLE="LIBIT Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="Channel Coding Tools"
HREF="channel.html"><LINK
REL="PREVIOUS"
TITLE="Channel Coding Tools"
HREF="channel.html"><LINK
REL="NEXT"
TITLE="Convolutional Codes"
HREF="convcodes.html"></HEAD
><BODY
CLASS="SECTION"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>LIBIT Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="channel.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 5. Channel Coding Tools</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="convcodes.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECTION"
><H1
CLASS="SECTION"
><A
NAME="CHANNELS"
>5.2. Channels</A
></H1
><P
>     Channels are used to simulate transmission noise. Currently the additive white gaussian noise (AWGN) and binary symetric (BSC) channels are defined.
  </P
><P
>     The binary symetric channel is used simply by knowing the cross-over probablity, that is the probability for a bit to be inverted during transmission. To simulate transmission over a BSC channel, use the <A
HREF="man.channel-bsc.html"
>channel_bsc()</A
> function.
  </P
><DIV
CLASS="EXAMPLE"
><A
NAME="CHANNEL-EXAMPLE-BSC"
></A
><P
><B
>Example 5-2. BSC channel example</B
></P
><PRE
CLASS="PROGRAMLISTING"
>  /* generate a random message of ten equiprobable bits */
  bvec message = source_binary(10, 0.5);

  /* send over a BSC channel of cross-over probability 0.1 */ 
  bvec received = channel_bsc(message, 0.1);
  </PRE
></DIV
><P
>     The AWGN channel is parametrized by the standard deviation of the additive white noise added during transmission. To simulate transmission over an AWGN channel, use the <A
HREF="man.channel-awgn.html"
>channel_awgn()</A
> function.
  </P
><DIV
CLASS="EXAMPLE"
><A
NAME="CHANNEL-EXAMPLE-AWGN"
></A
><P
><B
>Example 5-3. AWGN channel example</B
></P
><PRE
CLASS="PROGRAMLISTING"
>  /* generate a random message of ten equiprobable bits */
  bvec message = source_binary(10, 0.5);
  /* modulate the message using BPSK (0 =&#62; -1, 1 =&#62; +1) */
  vec modulated = modulate_bpsk(output);
  /* send over an AWGN channel of standard deviation 0.5 */ 
  vec received = channel_awgn(message, 0.5);
  </PRE
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="channel.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="convcodes.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Channel Coding Tools</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="channel.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Convolutional Codes</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>